Fuel feed and charge forming method and apparatus

ABSTRACT

The disclosure embraces a fuel feed and charge forming method and apparatus wherein the apparatus is of comparatively small size particularly for use with chain saws and other motor driven tools to effect the reduction in weight. The charge forming apparatus embodies a Venturi construction of modified shape, providing a method of operation wherein high capacity delivery of fuel and air mixture to the engine is attained, the mounting means for the charge forming apparatus being of a character to reduce the transmission of engine heat to the apparatus.

United States Patent 1 Van Camp et a1.

[451 July 17, 1973 FUEL FEED AND CHARGE FORMING METHOD AND APPARATUS[75] Inventors: Robert L. Van Camp; Bernard C.

a Phillips, both of Toledo, Ohio [73] Assignee: Borg-Warner Corporation,Chicago,

[22] Filed: Mar. 2, 1972 [21] Appl. No.: 231,169

Related U.S. Application Data [63] Continuation of Ser. No. 14,781, Feb.27, 1970, abandoned, which is a continuation of Ser. No. 742,679, July5, 1968, abandoned.

[52] U.S. C1 261/35, 261/78 R, 261/69 A, 26l/DIG. 68

[51] Int. Cl F02m 17/04 [58] Field of Search 261/69 A, DIG. 68, 261/37,41, 78 R; l23/D1G. 6, 73 R, 139.8 AH

[56] References Cited UNITED STATES PATENTS 4/1919 Mathis 165/52 6/1927Banerey 261/41 6/1937 Chandler 285/41 2,154,033 4/1939 Cameron 261/1382,343,815 3/1944 Snyder.. 261/50 2,456,626 12/1948 Dahnke. 138/443,065,957 11/1962 Phillips 261/D1G. 68 3,133,129 5/1964 Phillips26l/D1G. 68 3,141,048 7/1964 Schneider 261/41 3,272,143 9/1966 Rice417/69 3,453,994 7/1969 Nutten et al.. 123/73 3,353,525 11/1967 Nuttenet a1 123/119 Primary Examiner-Tim R. Miles Attorney-Harry O. Ernsberger[57] ABSTRACT The disclosure embraces a fuel feed andcharge formingmethod and apparatus wherein the apparatus is of comparatively smallsize particularly for use with chain saws and other motor driven toolsto effect the reduction in weight. The charge forming apparatus embodiesa Venturi construction of modified shape, providing a method ofoperation wherein high capacity delivery of fuel and air mixture to theengine is attained, the mounting means for the charge forming apparatusbeing of a character to reduce the transmission of 'engine heat to theapparatus.

5 Claims, 9 Drawing Figures PAIENTEU 1 3.746.320

. sum 2 OF 2 x 1 E by? Fig.9

FUEL FEED AND CHARGE FORMING METHOD AND APPARATUS This is a continuationof copending application, Ser. No. 14,781, filed Feb. 27, 1970, nowabandoned, which is a continuation of Ser. No. 742,679, filed July 5,1968 and now abandoned.

The invention relates to a fuel feed and charge forming method andapparatus for supplying a fuel and air mixture to internal combustionengines of the twocycle type of a character employed for driving chainsaws, lawnmowers, outboard marine engines and the like wherein the fuelfeed and charge forming apparatus involves a diaphragm type carburetorand diaphragm fuel pump which are combined in a unitary construction.

Heretofore carburetors of the diaphragm type have been utilized,particularly for use on chain saws, and the carburetor body constructionhas been fashioned of a size to provide a mixing passage of crosssectional area to accommodate air and fuel mixture in volumes adequateto operate engines of low horsepower of the two-cycle type. Carburetorand fuel pump combinations have been devised with a view effectingreduction in weight of the carburetor construction particularly for useon chain saws because it is desirable insofar as possible to reduce theweight of a portable chain saw. An example of this type of carburetor isdisclosed and claimed in Phillips U.S. Pat. No. 3,275,306. Afurtherfactor in the construction of a carburetor and fuel pump combinationparticularly for use with a chain saw is the limited space available forinstallation of the carburetor and fuel feed apparatus. The carburetorshown in U.S. Pat. No. 3,275,306 has been commercially produced and usedextensively with chain saw engines. The size of the carburetors madeaccording to the disclosure of this patent is about 1% X 1% X 1% incheswhich, at the time of the development of the invention disclosed in U.S.Pat. No. 3,275,306 was considered to be a very compact construction, thecombined fuel pump and carburetor of the character shown in the patentweighing about 5 ounces.

The present invention embraces a combined carburetor and fuel pumpconstruction which is very small and compact and yet provides aconfiguration of mixing passage facilitating a high volume flow of airand fuel mixture adequate to operate chain saw engines or engines of asimilar character efficiently at all speeds.

An object of the invention resides in a method of forming a combustiblefuel and air mixture and obtain" ing a high volume flow thereof byestablishing a region of reduced pressure in the mixing passageeffective to increase the mixture flow as compared with a conven' tionalconfiguration of mixing passage and to provide a more homogeneousmixture of fuel and air for the engmc.

Another object of the invention resides in the provi sion of acarburetor and fuel pump construction which is of reduced size andwherein the arrangement for mounting the construction is of a characterto minimize the transmission or conduction of engine heat to thecarburetor body thereby minimizing the tendency for the liquid fuel inthe fuel chamber of the carburetor to be volatilized.

The invention has for an object the provision of a comparatively smallcompact carburetor fashioned with a mixing passage embodying a novelform of mm turi-like shape which promotes an increase in volumet ric airand mixture flowcapacity with improved distribution of the fuel in theairstream in a mixing passage of substantially reduced size.

Another object of the invention resides in a carburetor constructionhaving a venturi-like configuration at the air inlet region, and amember exteriorly of the car buretor body movable to a position toobstructthe air inlet region for use in engine starting operations.

Further objects and advantages are within the scope of this inventionsuch as relate to the arrangement, operation and function of the relatedelements of the structure, to various details of construction and tocombinations of parts, elements per se, and to economics of manufactureand numerous other features as will be apparent from a consideration ofthe specification and drawing of a form of the invention, which may bepreferred, in which:

FIG. 1 is a side elevational view, partly in section, of a chain sawconstruction powered by a two-cycle engine illustrating one form of thecharge forming and fuel feed apparatus of the invention associatedtherewith;

FIG. 2 is a top plan view of the combined carburetor and fuel pumpconstruction embodying the invention;

FIG. 3 is a view of one side of the construction shown in FIG. 2;

FIG. 4 is a view of the air inlet end of the construction;

FIG. 5 is an elevational view of the opposite side of the carburetor andfuel pump construction;

FIG. 6 is a view of the opposite or mixture outlet end of thecarburetor;

FIG. 7 is an enlarged longitudinal sectional view through the carburetoron the longitudinal axis of the mixing passage;

FIG. 8 is an enlarged transverse sectional view, the section being takensubstantially on the line 8 8 of FIG. 2, and

FIG. 9 is an enlarged sectional view taken substam tially on the line9-9 of FIG. 8. i

The diaphragm carburetor and pump construction embodying the inventionis of a character particularly usable with low horsepower two cycleengines and more especially engines employed for powering chain saws,lawnmowers, portable drills and wherever a compact lightweightcarburetor and pump construction is desired.

The carburetor and fuel pump construction has par ticular utility foruse with chain saws where it is impera tive to reduce weight, thecarburetor construction being of a character which is operable in allangular positions, including inverted position, a necessary requisitefor chain saw operation. FlGd. 2 through 6 illus trate the carburetorand fuel pump combination of actual siae employed with two-cycle chainsaw engines.

Referring to the drawings in detail and initially to FIG. 1, there isillustrated an internal combustion en gine driven chain saw ofconventional construction cmbodying a form of charge forming and fuelfeed apparatus of the invention. The saw construction is inclusive of ahousing It) enclosing frame means (not shown) and an engine 12 of the,reciprocating piston two-cycle type. The engine 12 includes a crankcasel4 and a cyl inder la, the walls of the cylinder being fashioned withcooling fins 1'7.

The engine embodies a conventional crankshaft I8 journalcd in thecrankcase l4 and a piston 19 reciprm cable in the cylinder 16, thepiston having a piston pin 20 connected by a connecting rod 21 with acrankpin 22 of the crankshaft 18.

The head of the cylinder is equipped with a spark plug (not shown) forigniting the fuel and air mixture in a combustion chamber or region 24above the piston 19.

The engine is provided with a port or passage (not shown) for conveyingfuel and air mixture from the crankcase 14 into the combustion chamber24 in a manner conventional in two cycle engines. The cylinder isprovided with an exhaust port (not shown) of conventional type throughwhich exhaust gases are exited from the cylinder after each power strokeof the piston.

The chain saw construction is equipped with handles or hand grip members26 and 28 to facilitate manipulation of the chain saw by an operator.Secured to the frame construction and extending forwardly is a platelikemember 30 which provides a support and guide means for an endless orchain type saw 32, illustrated schematically in FIG. 1, the forward endof the member 30 journally supporting a conventional sprocket (notshown) engaging and guiding the chain saw.

The saw chain engages a driving sprocket (not shown) driven by theengine crankshaft 18 through an automatic clutch mechanism (not shown).The automatic clutch mechanism is of a conventional type whichautomatically establishes an operative drive connection between thecrankshaft l8 and the saw chain drive sprocket at normal or high enginespeeds, the clutch mechanism automatically disconnecting the driveconnection with the crankshaft 18 when the engine speed is reduced toidling speed. The construction and operation of the chain saw areconventional.

The fuel feed system and charge forming apparatus includes diaphragmcarburetor and diaphragm fuel pump construction shown in FIGS. 2 through9. The carburetor component is inclusive of a carburetor body 36, whichis preferably of die cast metal, the actual size of the body beingillustrated in FIGS. 2 through 6. The body is of generally cubical shapeand is fashioned with an air and fuel mixing passage 38, shown in FIG.7, the passage having an air inlet region 40 and a mixture outlet region42.

The mixing passage includes a modified venturishaped configuration whichwill be hereinafter described in detail, the air inlet region beingdefined by a curved configuration 43. The mixture outlet end of thecarburetor has a uniplanar mounting surface 45 which, as shown in FIGS.1 and 5, is adapted for attachment to an intake manifold 46 forconveying fuel and air mixture into the engine crankcase 14. As shown inFIG. I, a conventional reed valve construction 48 controls delivery ofmixture into the crankcase. A gasket 50 is disposed between thecarburetor body and the intake manifold 46.

The housing construction includes a cover portion 52 having an air inletpassage in which is disposed an air filter 54 to filter air admitted tothe air inlet 40 of the carburetor. .lournaled in bores in the walldefining the mixture outlet region 42 of the mixing passage is athrottle shaft 56. The region of the throttle shaft within the mixtureoutlet 42 has a flat surface 57 on which is mounted a disc-type throttlevalve 58.

The throttle shaft 56 is provided with a central threaded bore toreceive a screw 59 securing the throttle valve 58 to the shaft 56, awasher 60 being disposed between the head of the screw 59 and thethrottle valve 58.

A portion of the throttle shaft exteriorly of the carburetor body isequipped with a plate 61 having openings 62 for accommodating an end 63of a throttle operating rod 64, shown in FIG. I. A threaded boss 65 on apump cover plate 132 supports a screw 66 engageable with the plate 61for adjusting the engine idling position of the throttle valve 58.Pivotally mounted on the hand grip portion 26 is a pin 67 pivotallysupporting a throttle valve actuating member or trigger 68 connectedwith the rod 64 whereby the operator manipulates the throttle valvethrough pivotal movement of the member 68. A spring 69 surrounding thethrottle shaft 56 normally biases the member 61 in a direction tomaintain the throttle valve 58 in near closed or engine idling position.

The curved surface 43 defining the air inlet 40 of the mixing passage isin the shape of a partial section of a torus, which configurationfacilitates smooth flow of air into the mixing passage, the curvedsurface 43 being also referred to as a curved surface of revolution.Means is provided independent of the carburetor for temporarilyobstructing the air inlet 40 for engine starting purposes. As shown inFIG. 1, a wall 70 of the chain saw housing 10 is fashioned with anopening slidably accommodating a rod 71 having a partially sphericallyshaped or dome-like closure member 72 mounted on the end of the rodadjacent the air inlet region 40.

The spherically shaped surface 73 of the member 72 is adapted, whenengaged with the surface 43 of the air inlet region to close or obstructthe air inlet region as a choke means for engine starting purposes. Therod 71 extends through the opening in the housing wall 70 and through anopening in a guide member or bracket 77 and has a button or enlargedportion 74 provided on the end thereof.

Disposed between the button member 74 and the wall 70 is an expansivecoil spring 75 which normally biases the rod in a direction to move theair inlet closure member '72 away from the inlet region whereby the airinlet region is normally open. A pin 76 extends through a transverseopening in the rod 71 and forms an abutment engaging the bracket 77 tolimit the extent of movement of the closure member 72 in a directionaway from the air inlet region of the carburetor. The member 72 may be aflat plate and, if desired, may be slidable transversely for opening andclosing the air inlet region in a well known conventional manner.

The mounting means for securing the carburetor to the mixture manifold46 is of a character minimizing the transmission or conduction of heatfrom the engine crankcase wall to the carburetor body. Fashioned on theexterior of the carburetor body 36 at the end of the carburetor adjacentthe air inlet region 40 are laterally projecting boss portions 79 whichare provided with bores 80, the manifold 46 being provided with threadedbores 81 to receive the threaded portions of the securing or mountingbolts 82 and 82a.

As shown in FIGS. 3 and 5, the boss portions 79 are of a lengthpreferably slightly less than one-third of the length of the carburetorbody, viz, the boss portions being of a length of about five-sixteenthsof an inch. Fashioned in one exterior side wall of the body is asemicylindrical recess 83 extending from the boss 79 to the mountingface 45 of the carburetor. The radius of curvature of thesemicylindrical recess 83 is substantially the same as the radius of thebores 80 so as to accommodate the bolt 82 in the manner illustrated inH6. 5.

The opposite side of the carburetor body is fashioned 'with a portion 85provided with a semicylindrical recess 86 of the same radius ofcurvature as that of the curved surface 80 to accommodate the othermounting bolt 82a. As shown in FIG. 3, the boss portion 85 containingthe semicylindrical recess 86 is of a length substantially equal to thelength of a boss 79. As shown in FIGS. 3 and 6, the carburetor body 36is fashioned with a generally rectangular recess 90 to effect reductionin weight of the carburetor body and to further reduce transmission ofengine heat to the body from the bolt 82a.

By providing the semicylindrical recess 83 on one side of the carburetorbody and a semicylindrical recess 86 and the rectangular recess 90 on,the opposite side of the carburetor body, there is a minimum area ofengagement of the mounting bolts 82 and 82a with the carburetor body andthe exposure of substantial portions of the bolts 82 and 82a to theambient air effect a cooling of the bolts resulting in a reduction inheat transferred or conducted to the carburetor body from the engine.

A feature of the carburetor involves a shape or configuration for themixing passage which, although resembling generally a venturi, involvesa special or mad ified configuration which, among other advantages,provides for an increased fluid flow through a restricted region of themixing passage of reduced diameter, this feature enabling a substantialreduction in size and weight of the carburetor and yet attain increasedvolumetric or air flow efficiency.

The actual size of the carburetor body as shown in FIGS. 2 through 6, isapproximately of the following dimensions: 1% inches in length, 1%inches in height excluding the thickness of the pump plate 132 and thediaphragm cover 119, and excluding protruding portions of the bosses'79, is about 15/l6 inches in width. The particular configuration orshape of the mixing passage is illustrated in FIG. 7. The curvature ofthe surface 43 defining the air inlet 40 is derived as a surface of revolution of a radius 93 about a circular line in a plane A--A normal tothe longitudinal axis B- -B of the mixing passage.

The terminus of the curved surface 43 converges or blends into the flator planar surface 94 at the air inlet end of the carburetor. Thisfeature enables the smooth flow of air into the air inlet region 40,this being an other factor increasing the air flow efficiency or capacity of the mixing passage. The diameter of the most re stricted regionor choke band 95 of the venturi like shape is indicated by dimension aswhich, in the carbu retor illustrated, is approximately thrce eighths ofan inch.

it is to he understood that while the diameter of the restricted zone 95in the mixing passage illustrated is about three-eighths of an inchwhich is the size required to accommodate air flow or volume of air fora particular size engine, the restricted band 95 may be of slightlylesser or greater dimension to accommodate engines of different sizeswithin the limitations of the size of the carburetor. Hence, thediameter 96 of the restricted zone 95 may be within a range of fivesixteenths inch and sevemsixtccnths inch without in creasing the overalldimensions of the carburetor body.

In the embodiment disclosed the choke band or restricted region is aboutone-sixteenth inch in width but may be of slightly greater width, theband terminating at the traverse plane 97. in the embodimentillustrated, the downstream curvature is generated as a surface ofrevolution of a radius 109 about a circle in the terminal plane 97defining the length of the choke band 95 and is a partial section of atorus in shape. The downstream terminus of curvature 100 is joined withthe cylindrical surface of the mixture outlet region 42 by an angular orfrusto-conical surface 112, the an gularity of taper of the surface 112being about 45 with respect to the longitudinal axis B-B of the mixingpassage. The small diameter of the curvature 100 at the plane 97defining the length of the choke band is of slightly greater diameterthan the: diameter 96 of the choke band.

This increase in diameter provides an annular recess or space adjacentthe terminus 97 of the choke band 95 of a depth or thickness indicatedat 104 of from fivethousandths of an inch to eight-thousandths of aninch and preferably about six-thousandths of an inch.

Thus, the annular enlargement provided at the region or zone ofintersection of the curvature 100 with the terminal plane 97 of thechoke band 95 providesan an nular region of reduced pressure, and themain orifice 106 provided by a passage 107 in the carburetor fuelchannel system, opens into this annular region of reduced pressure.

The feature of delivering fuel for normal and high speed engineoperation through the main orifice 106 into the annular or circular zone102 of reduced pres sure adjacent the terminal plane 97 of the chokeband promotes a more homogeneous mixture of fuel and air. The annularregion 102 of reduced pressure influences the fuel delivered from theorifice 10610 migrate or move circularly in the annular none 102 ofreduced pressure thereby minimizing the tendency for the fuel to bedelivered into the central region or core of the air stream movingthrough the area defined by the choke band.

It is found that this tendency for the fuel to migrate or spread aroundthe circular zone 102 of reduced pressure fosters improved mixing of theliquid fuel with the air flowing through the mixing passage so that amore homogeneous combustible mixture is attained. This factor increasesthe efficiency of the engine through improved homogeneity of the mixtureby reason of the method of delivering the fuel from the orifice llltiinto an annular reduced pressure zone in the mixing passage.

An important factor providing increased efficiency of mixture flowthrough the mixing passage resides in the downstream curvature 100 ofthe passage wall. By fashioning the surface 100 as a surface ofrevolution about a circle in the plane 97, the fuel and air mixturetends to flow smoothly along and in contact with the curved surface 100without turbulence as the mixture expands after moving through therestricted zone 95.

In a conventional vcnturi shape, the surface downstream of therestricted zone or choke band is of frustoconical shape providing aprogressive increase in cross section of linear character. The curvedsurface of revolution 100 provides a nonlinear or accelerated increasein cross sectional area at succeeding equal increments of distanceaxially of the mixing passage downstream of the ledge 102. Thisfacilitates progressively accelerated increase in expansion of the fueland air mixture providing improved flow efficiency and increaseddelivery of mixture into the engine.

In the carburetor arrangement of the invention, it is imperative thatthe main fuel delivery orifice 106 open into the mixing passage at aregion downstream of the terminal plane 97 of the choke band 95 and asclose as practicable to said plane in order to obtain the advantage ofthe reduced pressure zone tending to spread the fuel in the air streammoving through the choke band Q5.

The carburetor of the invention embodies a main or primary fuel deliverysystem for normal and high speed engine operation and an engine idlingand low speed secondary fuel delivery system which are similar to thesystems disclosed in Phillips US. Pat. No. 3,275,306. The carburetorbody is fashioned with a circular recess or fuel chamber 1 15, shown inFIGS. 7, 8 and 9, a flexible member or diaphragm l 17 extending acrossthe recess forming one wall of the fuel chamber 115. A gasket 118 isdisposed between the periphery of the diaphragm and the planar surfaceof a portion of the carburetor body defining the fuel chamber 115.

A cover member 119 is disposed beneath the diaphragm and has a centraldepressed region to facilitate flexing of the diaphragm, the cover 119being provided with a vent opening 120.

Screws 122 extend through registering openings in the cover 119,diaphragm 117 and gasket 118 and are threaded into openings in the body36 to secure these parts in the positions shown in FIGS. 7 and 8. Thediaphragm 117 is adapted to be flexed or actuated by reduced pressure orengine aspiration in the mixing passage 38 for controlling delivery ofliquid fuel into the unvented fuel chamber 115.

The body 36 is fashioned with a fuel inlet passage 124 in which isdisposed a fuel filter or screen 125. The duct or passage 124 is incommunication with a fuel delivery channel 127 of a fuel pumpconstruction 128 of the character shown in Phillips U.S. Pat. No.3,275,306. The pump includes a pumping diaphragm 130, a cover member orplate 132, a fuel chamber 133 formed in the body 36 at one side of thediaphragm and a pulse or pumping chamber 135 formed in the cover plate132.

The pulse chamber 135 is connected with a pulse channel 138 which opensat the mounting face 45 and registers with an opening in the crankcasewall whereby varying fluid pressure in the engine crankcase flexes orvibrates the pumping diaphragm 130 to pump fuel from a supply to thecarburetor. A nipple 140, extending into an opening in the carburetorbody is connected by a tube (not shown) with a fuel tank. The pumpingdiaphragm 130 is fashioned with flap valves (not shown) cooperating withports incommunication with the fuel chamber 133 whereby fuel is pumpedunder comparatively low pressure to the inlet passage 124 in thecarburetor.

As shown in FIG. 8, a bore 142 in the carburetor body accommodates avalve body or member 143 slidably disposed therein. The valve body 143is of polygonal cross section and is fashioned with a needle valveportion I44 cooperating with a port 145 opening into the inlet duct I24.

Fulcrumed on a pin I47 and disposed in the fuel chamber is a lever 149,the long arm of the lever engaging a button-like member secured to thecentral region of the diaphragm and extending through reinforcing discs151 and 153.

The short arm of the lever is engaged with the lower end of the valvebody 143. An expansive coil spring 155 engages the long arm of the leveradjacent the fulcrum, the spring normally biasing the valve 144 to aposition closing the port 145. Through this arrangement the valve body143 is responsive to the flexing movements of the diaphragm 117.

The main or primary fuel delivery system is inclusive of the mainorifice 106, being the outlet of passage 107, the latter being incommunication with a well 157. Disposed between the passage 107 and thewell 157 is a fuel wettable member 158, such as a fine mesh screen,whereby the liquid fuel adhering to the screen by capil' lary actionforms a liquid or capillary seal to prevent back bleeding of air throughthe main orifice into the secondary fuel delivery system when the lattersystem is delivering fuel into the mixing passage. The principle of acapillary or liquid fuel seal for the prevention of back bleedingthrough the main orifice is described in Phillips US. Pat. No.2,841,372.

The capillary or liquid seal is readily broken or overcome upon increasein engine speed by reason of the increase in aspiration or reducedpressure in the mixing passage with the throttle open, thusreestablishing fuel delivery through the mainorifice 106 forintermediate and high speed engine operation.

The body 36 is fashioned with a bore 160 having a threaded portion toreceive a threaded body of an adjusting valve member 162, the member 162having a needle valve portion 163 which extends into a restrictedpassage 164 opening into the well or recess 157.

The valve body 162 is provided with a knurled manipulating head 165, anda coil spring 166 between the head and the carburetor body providingfriction to retain the valve body in adjusted position. The bore 160 isin communication with the fuel chamber 115 by a passage 167, shown inbroken lines in FIG. 9. Fuel for normal and high speed engine operationflows from the diaphragm the] chamber 115 through passage 167, bore 160,past the needle valve 163, through restriction 164 and well 157 fordischarge through the main orifice 106 provided by the passage 107.

The secondary fuel delivery system for engine idling and low speedoperation includes a supplemental chamber 170 which is in communicationwith the mixing passage 38 by way of an engine idling orifice 171 and alow speed orifice 172. The body 36 is fashioned with a bore 174 having athreaded portion to accommodate a threaded portion of a valve body 175.The valve body 175 has a tenon provided with a needle valve portion17''! extending into and cooperating with a restricted passage 178 whichopens into a recess 179 of the fuel chamber 115.

The supplemental chamber 170 is connected with the bore 174 by a passage18! shown in FIG. 9. The valve body 175 is fashioned with a knurledmanipulating head 183, and a coil spring 184 is disposed between thehead 183 and the carburetor body 36 providing friction for retaining thevalve body 175 in adjusted position.

The operation of the carburetor is as follows: Assuming that thecarburetor has been previously operated and the fuel chamber 115 isfilled with liquid fuel which had been pumped from the supply tank bythe diaphragm pump construction 128 to the region of the inlet valve144. The pumping diaphragm is actuated by varying fluid pressure fromthe engine crankcase when the engine is cranked or started. In startingthe engine, the operator exerts pressure on the button 74 on the rod 71and thereby moves the partial spherically shaped member 72 intoengagement with the curved surface 43 to substantially close the airinlet 40 of the mixing passage 38.

The engine is then cranked by the operator with the throttle valve 58 inpartial or full open position. With the air inlet 40 substantiallyclosed by the member 72, engine aspiration in the mixing passage iseffective to aspirate fuel from the fuel chamber 115 past the needlevalve 163 through the well 157 and passage 107, the fuel beingdischarged through the main orifice 106, thus starting the engine.

As soon as the engine is operating, the operator removes manual pressurefrom the button 74 and the spring 75 retracts the member 72 away fromthe surface 43 thereby opening the inlet 40.

In normal or high speed operation of the engine, the fuel aspirated intothe mixing passage through the main orifice 106 enters the mixingpassage at the annular region of reduced pressure provided at the region102 adjacent the choke band 95 of the venturi-like configuration.

Through this method of delivering the fuel into an annular region ofreduced pressure in the mixing passage, the fuel is more uniformly mixedwith the air moving through the mixing passage to provide a homogeneousmixture of fuel and air. The aspiration in the mixing passage isinfluential through the main orifice passage 107, fuel well 157 and fuelchannels 164, 160 and 167 to establish reduced pressure in the fuelchamber 115.

Reduced pressure established in the fuel chamber 115 flexes thediaphragm upwardly, as viewed in FIG. 8, swinging the lever 149 aboutthe fulcrum 147 in a counterclockwise direction whereby the inlet valve144 moves downwardly and opens the inlet port 145 to effect flow of fuelinto the chamber 115 at the rate at which the fuel is aspirated into themixing passage from the fuel chamber 115 through the main orifice 106.The rate of fuel delivery through the main orifice is regulated orcontrolled by the manually operated needle valve 163.

When the throttlevalve 58 is in engine idling position, that is, in theposition shown in FIG. 7, fuelfor engine idling operation flows from thefuel chamber 115 through restricted passage 178, past the needle valve177, through bore 174, passage 177 into the supplemental chamber I70 andis delivered through the en gine idling orifice 171 at the downstreamside of the throttle valve 58.

During idling operation of the engine the liquid fuel adhering to themember or screen 158 prevents the back bleeding of air from the mixingpassage through the main orifice 106 and into the engine idling fucl systcm so as not to impair the delivery of fuel for engine idling purposes.

When the throttle valve 58 is partially opened, fuel llows from thesupplemental chamber 170 through both the engine idling orifice I'll andthe low speed orifice 172. The fuel for delivery through the secondaryorifices i7! and'l'72 is regulated or controlled by adjustment of theneedle valve 177.

The special configuration of mixing passage illustrated in FIG. 7 andhereinbefore described provides for increased flow of air and fuel tothe engine whereby a smaller size mixing passage may be used than hasheretofore been possible in carburetors of this general character.

It should be noted that the curvature 43 of the air inlet blends intothe planar face 94 of the carburetor facilitating smooth flow of airthrough the air inlet 40. The provision of the annular zone 102 ofreduced pres sure adjacent the choke band or zone of maximum restrictioneffects distribution of the fuel delivered through the main orifice 106in an annular region so that the fuel is more thoroughly mixed with theair moving through the mixing passage to provide a homogeneous mixturethereby improving engine efficiency.

Another factor providing for high air flow movement through the mixingpassage is that the mixing passage is of comparatively short lengthbetween the entrance face 94 and the mounting face 45. With thisarrangement there is less frictional drag upon the air with a consequentincrease in the air flow capacity of the mixing passage, this beinganother factor enabling the use of a mixing passage of reduced crosssectional dimensions capable of supplying'adequate volume of mixture forall engine speeds.

The use of the comparatively short bosses 79 engaging the mounting bolts82 provides clearance regions adjacent the mounting bolts for coolingthe bolts and additionally reduces the transmission or conduction ofheat from the engine crankcase to the carburetor body, thus minimizingthe tendency for volatilizing the liquid fuel in the fuel chamber. Thecarburetor of actual size, as shown in FIGS. 2 through 6, according tothe dimensions given herein weighs about 3 ounces.

The carburetor of the invention is of very small size and of much lessweight than other diaphragm carburetors of comparable flow capacity andthe method of mounting the carburetor reduces heat transfer to thecarburetor body. The comparatively short mixing passage of theconfiguration hereinbefore described substantially reduces air frictionor air drag with the consequent increase in flow capacity.

It is apparent that, within the scope of the invention, modificationsand different arrangements may be made other than as herein disclosed,and the present disclo sure is illustrative merely, the inventioncomprehending all variations thereof.

We claim:

1. Charge forming apparatus for aninternal combustion engine including,in combination, a substantially cubically shaped body provided with amixing passage having an air inlet region and a mixture outlet region, afuel chamber in the body, a flexible diaphragm forming a wall of thechamber, a fuel inlet in the body, a valve for the fuel inlet, controlmeans for said fuel inlet valve including a lever actuated by movementof said diaphragm under the influence of reduced pressure in the mixingpassage, a main orifice opening into the mix ing passage, a throttlevalve in the mixture outlet region of the mixing passage, an engineidling orifice opening into the mixing passage at the downstream side ofthe throttle valve, fuel channel means in said body for conveying liquidfuel from the fuel chamber to the orifices, said body having a planarmounting surface for mounting on an engine, a boss extendingtransversely from each side of the body at the end of the body adjacentthe air inlet region, each of the bosses having a bore accommodating amounting bolt, said bosses being spaced from the planar mounting surfaceand of a length less than one-third the length of the body whereby toexpose portions of the mounting bolts to the atmosphere for cooling thebolts.

2. Charge forming apparatus for an internal combustion engine including,in combination, a substantially cubically shaped body provided with amixing passage having an air inlet region and a mixture outlet region, afuel chamber in the body, a flexible diaphragm forming a wall of thefuel chamber, a fuel inlet passage in the cubically shaped body, anelongated valve member in said inlet passage longitudinally movable onan axis normal to the plane of the diaphragm, control means for saidvalve member including a lever actuated by movement of said diaphragmunder the influence of reduced pressure in the mixing passage, a mainorifice opening into the mixing passage, a throttle valve in the mixingpassage, an engine idling orifice opening into the mixing passage at thedownstream side of the throttle valve, fuel channel means in said bodyfor conveying liquid fuel from the fuel chamber to the orifices, saidbody having a planar mounting surface for mounting on an engine, a bossextending transversely from each side of the body at the end of the bodyadjacent the air inlet region, each of the bosses having a boreaccommodating a body mounting bolt, said bosses being spaced from theplanar mounting surface to expose portions of the mounting bolts to theatmosphere for cooling the bolts, each side of the body having a recessof semicircular cross section between the adjacent boss and the mountingsurface of the body accommodating a mounting bolt.

3. Charge forming apparatus including, in combination, a cubicallyshaped body provided with a mixing passage having an air inlet region, afuel and air mixing zone and a mixture outlet region, a fuel chamber inthe body, a flexible diaphragm forming a wall of the fuel chamber, afuel inlet in the body, valve means for the fuel inlet, control meansfor said valve means including a lever actuated by movement of saiddiaphragm under the influence of reduced pressure in the mixing passage,a main orifice opening into the mixing passage, a throttle valve in themixture outlet region of the mixing passage, an engine idling orificeopening into the mixing passage at the downstream side of the throttlevalve, fuel channel means in said body for conveying liquid fuel fromthe fuel chamber to the orifices, said air inlet region being defined bya first curved surface of revolution, the inner circular terminus ofsaid curved surface defining a circular zone of maximum restriction inthe mixing passage, a second curved surface of revolution having itssmall diameter adjacent the circular zone of restriction and defining awall portion of a fuel and air mixing zone of the mixing passage, thesmall diameter of the second curved surface being of greater diameterthan that of the circular zone of maximum restriction, said secondcurved surface of revolution being joined with a cylindrical surface ofthe mixing passage, said main orifice opening into the mixing passageadjacent the circular zone of maximum restriction.

4. The combination according to claim 3 wherein the circular zone ofmaximum restriction is of a diameter in a range of five-sixteenths inchand seven-sixteenths inch.

5. Charge forming apparatus including, in combination, a cubicallyshaped body provided with a mixing passage having an air inlet regionand a mixture outlet region, said body having a planar mounting surfacefor mounting on an engine, a fuel chamber in the body, a flexiblediaphragm forming a wall of the chamber, a fuel inlet in the body, valvemeans for the fuel inlet, control means for said valve means including alever actuated by movement of said diaphragm under the influence ofreduced pressure in the mixing passage, a main orifice opening into themixing passage, a throttle valve in the mixture outlet region of themixing passage, an engine idling orifice opening into the mixing passageat the downstream side of the throttle valve, fuel channel means in saidbody for conveying liquid fuel from the fuel chamber to the orifices,said air inlet region being defined by a curved surface of revolution,the inner circular terminus of said curved surface defining a circularzone of maximum restriction of the mixing passage, a second curvedsurface of revolution forming a wall portion of the mixingpassagedownstream of the air inlet region, the minimum diameter of the secondcurved surface of revolution being adjacent the inner terminus of thefirst curved surface, the largest diameter of the second curved surfacebeing joined with a cylindrical surface of the mixing passage, said mainorifice opening into the mixing passage at the region of minimumdiameter of the second curved surface of revolution, a transverselyextending mounting boss on each side of said body adjacent the air inletregion of the mixing passage, the bosses being about onethird the lengthof the body, each boss having a bore adapted to receive a bolt formounting the body, each side of the body having a recess of semicircularcross section between the adjacent boss and the mounting surface of thebody accommodating a mounting bolt.

i t I t

1. Charge forming apparatus for an internal combustion engine including,in combination, a substantially cubically shaped body provided with amixing passage having an air inlet region and a mixture outlet region, afuel chamber in the body, a flexible diaphragm forming a wall of thechamber, a fuel inlet in the body, a valve for the fuel inlet, controlmeans for said fuel inlet valve including a lever actuated by movementof said diaphragm under the influence of reduced pressure in the mixingpassage, a main orifice opening into the mixing passage, a throttlevalve in the mixture outlet region of the mixing passage, an engineidling orifice opening into the mixing passage at the downstream side ofthe throttle valve, fuel channel means in said body for conveying liquidfuel from the fuel chamber to the orifices, said body having a planarmounting surface for mounting on an engine, a boss extendingtransversely from each side of the body at the end of the body adjacentthe air inlet region, each of the bosses having a bore accommodating amounting bolt, said bosses being spaced from the planar mounting surfaceand of a length less than one-third the length of the body whereby toexpose portions of the mounting bolts to the atmosphere for cooling thebolts.
 2. Charge forming apparatus for an internal combustion engineincluding, in combination, a substantially cubically shaped bodyprovided with a mixing passage having an air inlet region and a mixtureoutlet region, a fuel chamber in the body, a flexible diaphragm forminga wall of the Fuel chamber, a fuel inlet passage in the cubically shapedbody, an elongated valve member in said inlet passage longitudinallymovable on an axis normal to the plane of the diaphragm, control meansfor said valve member including a lever actuated by movement of saiddiaphragm under the influence of reduced pressure in the mixing passage,a main orifice opening into the mixing passage, a throttle valve in themixing passage, an engine idling orifice opening into the mixing passageat the downstream side of the throttle valve, fuel channel means in saidbody for conveying liquid fuel from the fuel chamber to the orifices,said body having a planar mounting surface for mounting on an engine, aboss extending transversely from each side of the body at the end of thebody adjacent the air inlet region, each of the bosses having a boreaccommodating a body mounting bolt, said bosses being spaced from theplanar mounting surface to expose portions of the mounting bolts to theatmosphere for cooling the bolts, each side of the body having a recessof semicircular cross section between the adjacent boss and the mountingsurface of the body accommodating a mounting bolt.
 3. Charge formingapparatus including, in combination, a cubically shaped body providedwith a mixing passage having an air inlet region, a fuel and air mixingzone and a mixture outlet region, a fuel chamber in the body, a flexiblediaphragm forming a wall of the fuel chamber, a fuel inlet in the body,valve means for the fuel inlet, control means for said valve meansincluding a lever actuated by movement of said diaphragm under theinfluence of reduced pressure in the mixing passage, a main orificeopening into the mixing passage, a throttle valve in the mixture outletregion of the mixing passage, an engine idling orifice opening into themixing passage at the downstream side of the throttle valve, fuelchannel means in said body for conveying liquid fuel from the fuelchamber to the orifices, said air inlet region being defined by a firstcurved surface of revolution, the inner circular terminus of said curvedsurface defining a circular zone of maximum restriction in the mixingpassage, a second curved surface of revolution having its small diameteradjacent the circular zone of restriction and defining a wall portion ofa fuel and air mixing zone of the mixing passage, the small diameter ofthe second curved surface being of greater diameter than that of thecircular zone of maximum restriction, said second curved surface ofrevolution being joined with a cylindrical surface of the mixingpassage, said main orifice opening into the mixing passage adjacent thecircular zone of maximum restriction.
 4. The combination according toclaim 3 wherein the circular zone of maximum restriction is of adiameter in a range of five-sixteenths inch and seven-sixteenths inch.5. Charge forming apparatus including, in combination, a cubicallyshaped body provided with a mixing passage having an air inlet regionand a mixture outlet region, said body having a planar mounting surfacefor mounting on an engine, a fuel chamber in the body, a flexiblediaphragm forming a wall of the chamber, a fuel inlet in the body, valvemeans for the fuel inlet, control means for said valve means including alever actuated by movement of said diaphragm under the influence ofreduced pressure in the mixing passage, a main orifice opening into themixing passage, a throttle valve in the mixture outlet region of themixing passage, an engine idling orifice opening into the mixing passageat the downstream side of the throttle valve, fuel channel means in saidbody for conveying liquid fuel from the fuel chamber to the orifices,said air inlet region being defined by a curved surface of revolution,the inner circular terminus of said curved surface defining a circularzone of maximum restriction of the mixing passage, a second curvedsurface of revolution forming a wall portion of the mixing passagedownstream of the air inlet region, the minimum diameter of the secondcurved surface of revolution being adjacent the inner terminus of thefirst curved surface, the largest diameter of the second curved surfacebeing joined with a cylindrical surface of the mixing passage, said mainorifice opening into the mixing passage at the region of minimumdiameter of the second curved surface of revolution, a transverselyextending mounting boss on each side of said body adjacent the air inletregion of the mixing passage, the bosses being about one-third thelength of the body, each boss having a bore adapted to receive a boltfor mounting the body, each side of the body having a recess ofsemicircular cross section between the adjacent boss and the mountingsurface of the body accommodating a mounting bolt.